In some cognitive radio systems the secondary users need to sense the availability of the spectrum before it can access the spectrum. In such a case, the accuracy of the results of spectrum sensing is critical for both primary and secondary systems. Multi-antenna techniques have been discussed in the literature to enhance the performance (accuracy) of spectrum sensing. However, in many arrangements already set forth in the field, all antennas at the secondary receiver are used for spectrum sensing purposes, indicating that all RF chains at the secondary receiver have to be used.